Re: [avr-gcc-list] Bug in avr-libc or?

[Per Arnold Blåsmo]

Thanks to all for your responses!

I should have read the docs and the FAQ in the avr-libc manual better.

I also fount this article on the usage of volatile on the net. I might 
be of interest to read among others.

http://www.programmersheaven.com/articles/pathak/article1.htm


Regards 
Per A.



Flemming Gram Christensen wrote:

> Try declaring your variable "volatile".
>
> volatile uint8_t var;
>
> Now the compiler will know that the variable can be changed from other parallel 
> executions (i.e. interrupts).
>
> Only do it with "signal" variables as it hurts performance.
>
> Regards
>
>  
>
> > -----Original Message-----
> > From: Per Arnold Blåsmo [mailto:address@hidden 
> > Sent: 1. juni 2004 09:42
> > To: address@hidden
> > Subject: [avr-gcc-list] Bug in avr-libc or?
> >
> > Hi,
> >
> > I have been doing a program  and got into a problem with a while loop.
> >
> > Basically what I wanted to do was to do a while loop that 
> > waited until a variable changed and so go out of the while loop.
> > The variable was altered by a interrupt routine.
> >
> > What happen was that the variable in the while loop was 
> > copied into a register and the while loop did test the 
> > register instead of the variable.
> > Thereby never detecting any change of the variable done in 
> > the interrupt routine.
> >
> > I made a test program to show the result:
> >
> > avrtest.c :
> >
> > #include <avr/io.h>
> > #include <avr/signal.h>
> >
> > uint8_t var;
> >
> > SIGNAL(SIG_INTERRUPT0){
> > var = 0;
> > }
> >
> > int main(void){
> >
> > var = 1;
> >
> > while(var==1){
> > // do nothing but wait
> > }
> >
> > //Now do sometning
> > var = 2;
> > }
> >
> >